Mt. Snowdon, Yr Wyddfa to the locals, is crawling with tourists in the summer months. So Constable Evans isn’t unduly alarmed when a young female hiker goes missing for a few hours. She might have taken a wrong turn or even stormed off to hide after a tiff with her boyfriend.

The routine search turns more ominous when the village police find an underground bunker - complete with handcuffs and chains. Now, as he copes with wedding plans and a visit from his disapproving mother, Evans has a serious investigation on his plate, searching for a link between the still-missing girl and the eerie, empty chamber.

And when his own fiancee disappears, the case goes from ominous to terrifying …